Signal receiving apparatus for a vehicle control system

ABSTRACT

A signal receiving embodiment which is operative in a vehicle control system includes a conductive track with a pair of conductive continuous rails. At least one conductive member is connected between the rails, and a plurality of signals are present in the rails, only one signal of which is desired to be sensed. The signal receiving embodiment includes at least one signal receiving means which is aligned in a predetermined position relative to the rails such that potentials induced in the signal receiving means by the desired signal are in a series aiding relationship whereas there is no potential induced by the undesired signals or if signal potential is induced by the undesired signals, the induced signal potential is in a series opposing relationship relative to the signal receiving means.

United States Patent [191 Hoyler et al.

[ 1 SIGNAL RECEIVING APPARATUS FOR A VEHICLE CONTROL SYSTEM [75}Inventors: Robert C. Hoyler, Pittsburgh; Brian R. Slattery, TurtleCreek, both of Pa.; George M. Thorne-Booth, Tarzana, Calif.

[73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

[22] Filed: May 28, 1971 [21] Appl. No.: 147,806

521 u.s.ci. ..246/36, 179/82 511 int. Cl B6l|21/00 52 Field ofSearch246/34 cr, 8, 36;

[56] References Cited UNITED STATES PATENTS 3,694.751 9/1972 Takahashiet al .1 246/8 X RECEIVER [4 1 July 17,1973

Primary ExaminerGerald M. Forlenza Assistant Examiner-Goerge H. LibmanA!t0rneyF. H. Henson, R. G. Brodahl and Jack M. Arnold [57] ABSTRACT Asignal receiving embodiment which is operative in a vehicle controlsystem includes a conductive track with a pair of conductive continuousrails. At least one conductive member is connected between the rails,and a plurality of signals are present in the rails, only one signal ofwhich is desired to be sensed. The signal receiving embodiment includesat least one signal receiving means which is aligned in a predeterminedposition relative to the rails such that potentials induced in the sig'nal receiving means by the desired signal are in a series aidingrelationship whereas there is no potential induced by the undesiredsignals or if signal potential is induced by the undesired signals, theinduced signal potential is in a series opposing relationship relativeto the signal receiving means 5 Claims, 9 Drawing Figures Ptented- July17, 1973 3,746,857

3 Sheds-Sheet 5 I RECEIVER vv SIGNAL RECEIVING APPARATUS FOR A VEHICLECONTROL SYSTEM CROSS-REFERENCES TO RELATED APPLICATIONS The presentinvention is related to the invention covered by US. Pat. No. 3,526,378entitled Signalling System For Determining The Presence OfA TrainVehicle by George M. Thorne-Booth which is assigned to the assignee ofthe present invention.

BACKGROUND OF THE INVENTION It has for some time been the practice inthe operation of vehicle control signaling system to divide the vehicletrack into a plurality of signaling blocks that are electricallyinsulated from each other. However, more recent vehicle systems are nowusing welded or continuous tracks involving longer sections of railsthat are not adapted for the use of insulated joints, and as a resultvehicle detection is more difficult with such a vehicle control system.

In such a vehicle control system there are usually a plurality ofsignals flowing through the conductive continuous tracks, which signalsmay include a desired signal that is to be sensed in a particularsignaling block. However, in the particular signaling block there mayalso be present locally generated signals which are transmitted toadjacent signaling blocks and also propulsion currents which flowthrough the rails. It is desired to sense only the signal transmitted tothe particular signaling block and to eliminate the sensing of anyundesired signals, namely the locally transmitted signal and thepropulsion currents flowing through the rails.

SUMMARY OF THE INVENTION In accordance with the teachings of the presentinvention a signal receiving system is operative with a conductive trackwhich includes a pair of conductive continuous rails in which at leastfirst and second signals are present. There is at least one signalreceiving means positioned in a predetermined alignment relative to thepair of rails and signal potential is induced in the one signalreceiving means in response to the first signal, and in response to thesecond signal, signal potentials are one of not induced or induced in aseries opposing relationship.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic showing of asignaling system in which the signal receiving system of the presentinvention may be included;

FIG. 2 illustrates a first technique for coupling one of the signalreceivers to a typical short circuit member;

FIG. 3 illustrates a second suitable technique for coupling signalreceivers to a typical short circuit member;

FIG. 4 is a top view of the signal receiving system of FIG. 3 and whichincludes a signal transmitting loop;

FIG. 5 is a section of FIG. 4 taken along the lines V-V;

FIG. 6 is a schematic diagram illustrating two signal receiving meansmounted on a short circuit member;

FIG. 7 is a schematic diagram illustrating four signal receiving meanscoupled to the short circuit member;

FIG. 8 illustrates one suitable technique for coupling signal receiversto a track rail; and

FIG. 9 is a schematic representation of four signal receivers coupled tothe track rails.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I there is provided aschematic showing of one vehicle control signaling system in which thesignal receiving embodiment of the present invention may be operative.The vehicle control signaling system includes two conductive continuousrails 10 and 11 which may comprise a plurality of welded sections withno insulating joints between the sections. A vehicle (not shown) maytravel along the track. A plurality of shunt bars such as the conductorsor short circuit members l2 and 13 are connected between the rails 10and 11 to balance the propulsion currents flowing through the rails aswell as to provide a conductive path for the desired signal currents.The section of track between short circuit members is defined as a trackcircuit signaling block. At each short circuit member or track circuitsignaling block boundary there is included a signal receiving means suchas the signal receiving means 14 and 15 which are coupled to receivers16 and 17 respectively. Operative at each boundary there is also atransmitter and a loop antenna. For example, at the boundary defined bythe short circuit member 13 there is a transmitter 18 and a loop antenna19. The transmitter 18 provides a signal which flows through the antenna19 and which is termed the local signal and is depicted by the letter Lon the drawing. It is seen that the configuration of antenna 19 isinherently cooperative with the physical form of conductor 13 to resultin the local signal (L) being introduced into the rails with componentsof introduced signal potential acting in a series opposing relationshipin a circuit through conductor 13, but in a series aiding relationshipin a circuit through conductor 12 and through the conductor (not shown)at the other end of the signal block, to the right of conductor 13. Todiagrammatically illustrate this inherent cooperation, there is shown onthe drawing the polarities of voltage impressed upon the sections ofrail 10 and 11 by the sides of the rectangular loop antenna 19 which isparallel thereto, for an instantaneous signal condition, as well assolid line arrows representing signal flow and phantom line arrowsillustrating the counter balancing effect through conductor 13. Thereceiving antenna 15 is operative to sense the track signals at afrequency F2 which is flowing in the short circuit conductor 13 betweenthe rails 10 and 12. The track signal at frequency F2 which is flowingin the rails is provided by a remote transmitter, for example, thetransmitter 20 which couples the signal via the antenna 21 to thesections of rail on each side of the conductor 12. It is this signal ata frequency F2 which is desired to be sensed by the antenna or signalreceiving means I5 operative with the conductor I3. As was mentioned thecurrents L flowing through the conductor 13 from the transmitter 18 arein a series opposing relationship, however, the currents L flowingthrough the rails I0 and II induce a magnetic field which in turninduces signal potentials which may be sensed by the receiver 15. It isnecessary, therefore, to position the antenna 15 in a predeterminedalignment relative to the track rails or the short circuit member 13such that no signal potential is induced in the antenna 15 by the localfield generated by the current L flowing through the track rails.Specific alignments of the antenna 15 are described to illustrate howthe local field may not be sensed or if it is sensed the signals flowingin the antenna are then in a series opposing relationship.

In FIG. 2 there is illustrated one embodiment in which a signalreceiving means such as an antenna 21 is mounted on a short circuitmember 22. The lines of flux from the local field are depicted by thelines LF, and it is readily seen that the flux lines are in thedirection shown, by use of the right hand rule in relation to thecurrent L as shown in FIG. 1. It is seen that the antenna or coil 21 ispositioned such that its axis is orthogonal to the lines of flux LF.Therefore, no signal L due to the lines of flux FL is induced in thecoil 21. The signal from the remote transmitter which is to be sensed bythe coil 21 flows through the short circuit member 21 in a direction asillustrated by the arrow S, the lines of flux which are generated inresponse to the signal S are illustrated by the flux lines SF. The linesof flux SF intersect the coil 21 at an angle which is not orthogonal tothe axis of the coil 21, and therefore current is induced in the coil 21which flows in a direction as illustrated by the line 23. The coil 21 inturn is coupled to a receiver 24 which senses the remote or desiredsignal S. It is seen that in an arrangement as shown in FIG. 2 thepositioning of the coil 21 is very critical, since if the coil 21 ispositioned at any angle which is not orthogonal to the flux field LFcreated by the local signal L there is a limited amount of currentinduced in the coil 21 from the local transmission.

In FIG. 3 there is illustrated another embodiment for the positioning ofsignal receiving means on the short circuit member such that a desiredsignal S may be sensed and an undesired signal L which is induced inresponse to the flux lines generated by a local transmitter are notsensed. The lines of flux induced by the local transmitter are depictedby the lines LF and the lines of flux generated by the current from thedesired signal S are depicted by the lines of flux SF. In thisparticular embodiment the positioning of the antennas relative to theflux lines LF is not critical. In this embodiment there are included twoantennas or coils, namely the coils 24 and 25. These coils are mountedby suitable means to a short circuit member 26, with the only alignmentrequirement being that the coils 24 and 25 be aligned substantiallyparallel to one another relative to a plane of reference. The coil 24 isconnected to the coil 25 by a lead 27. The other lead of coil 24 isconnected to a receiver 28 and the remaining lead of the coil 25 is alsoconnected to the receiver 28. The potentials induced across the coils 24and 25 in response to the flux lines LF are illustrated by the plus andminus signs shown under the letters L which are adjacent to the coils 24and 25, respectively. The potentials induced across the coil 24 and 25in response to the flux lines SF are illustrated by the plus and minussigns under the letter S adjacent to the coils. It is seen in tracingthe potential drop across the two coils due to the field LF that acrossthe coil 24 there is a potential drop of +L, and across the coil 25there is a potential drop of L induced. Therefore, there is a resultantpotential drop of zero sensed by the receiver 28 in response to the fluxfield LF. Across coil 24 there is a potential drop of S due to thedesired signal S, and a potential drop of S across the coil 25 due tothe desired signal S, resulting in a potential drop of 2S being sensedby the receiver 28. It is seen therefore, that the receiver 28 does notsense any potential induced by the local field LF due to the cancellingeffect or series opposing relationship of the signal L in the two coils24 and 25. However, the receiver 28 senses the desired signal 5 sincethere is a series aiding relationship of the potential drop across thecoils 24 and 25 due to the lines of flux SF resulting in the signal 2Sbeing sensed by the receiver 28.

In FIG. 4 there is illustrated a top view of the coils 24 and 25 of FIG.3 and their position relative to the conductor 26. There is alsoillustrated a loop antenna 29 which induces the local field LF about thecoils 24 and 25. The flow of current through the loop antenna 29 isillustrated by the arrows L, and the lines of flux LF generted bythe'current flowing in the loop antenna 29 are illustrated by the dotsand Xs LF wherein X depicts the lines of flux entering the plane of thedrawing and the dots depict the lines of flux exiting the plane of thedrawing. That the lines of flux are in the direction shown is readilyapparent by the use of the right hand rule. The current provided by thedesired signal S is shown by the arrows S.

FIG. 5 is a section of FIG. 4 taken along the line VV. This figure is aclearer representation of how the lines of flux actually intersects thecoils 24 and 25 and how the resulting signal potentials are produced.The potential drop induced across the coils 24 and 25 due to the localfield lines of flux LF are depicted by the plus and minus signs directlybelow the letter L which is adjacent each coil. The potential dropinduced across the coils 24 and 25 due to the desired signal S lines offlux SF is indicated by the plus or minus signs directly below theletters S adjacent the coils. In tracing the cur rent flow from thereceiver 28 through the coils and back to the receiver in acounterclockwise direction it is seen that the potential drop due to thelocal field LF is +L across the coil 24, and L across the coil 25 whichresults in a series opposing relationship and a net resultant potentialdrop of 0 being sensed by the receiver 28. Following signal flow throughthe coils in the same direction due to the desired field of flux SFthere is a potential drop of S across the coil 24, and S across the coil25 resulting in a net potential drop of 2S being sensed by the receiver28. It is seen therefore that the particular coil arrangement shownresults in the cencellation of substantially all of the signal potentialdue to the local field LF.

In FIG. 6 there is shown a short circuit member 30 which has two signalreceiving antennas or coils 31 and 32 mounted on each end and on theopposite sides of the short circuit member 30. This is required insystems where a return for the propulsion currents is connected to thecenter of the short circuit member. In addition to the local field LFand the desired signal field SF being present there is also a signalfield NF which is generated by the propulsion currents N which flowthrough the rails. Since the propulsion currents in the rails flow inthe same direction in each rail there are lines of flux produced in onedirection at one end of the short circuit member and in the oppositedirection at the other end of the short circuit member. This is seen bythe arrows NF as shown in the drawing, and it is readily seen that theflux lines NF are in the direction shown, by use of the right hand rulein relation to the currents N as shown in FIG. 1. The signal potentialinduced in the coils 31 and 32 'due to each of the flux fields isillustrated under the letters S, L and N respectively which are adjacentto the coils 31 and 32. In tracing the potential drop due to the localfield LF it is seen in tracing the flow of a counterclockwise directionthat the potential drop across the coil 31 is +L and the potential dropacross the coil 32 is L which results in a potential drop of zero beingsensed by the receiver 33. In tracing the potential drop due to thepropulsion currents which is illustrated by the flux lines NF, thepotential drop across the coil 31 is +N and the potential drop acrossthe coil 32 is +N which results in the receiver 33 sensing a potentialdrop of 2N. Therefore the receiver 33 must include crystal filters orsome such device, as shown in FIG. 7 of the referenced US. Pat. No.3,526,378, to allow the passage of only the desired signal into thereceiver and to block the signal potential 2N generated by thepropulsion current. Tracing the potential drop across the coils for thedesired signal S there is a potential drop of S across the coil and Sacross the coil 32 resulting in a potential drop of -28 being sensed bythe receiver 33.

In FIG. 7 there is shown an antenna or coil embodiment in which thepotential drops generated by the noise field NF due to the propulsioncurrent N are cancelled which in turn reduces the need for filters inthe receiver which is coupled to the antenna arrangement. A shortcircuit member 34 has mounted thereon coils 35, 36, 37 and 38. Thesecoils are connected together in a predetermined relationship such thatthe potentials induced across the coils due to the desired flux field SFare in a series aiding relationship whereas the potentials inducedacross the coils due to the local field LF and the noise field NF are ina series opposing relationship. The lines of flux due to the localfields are depicted by the lines LF, the lines of flux due to the noisefield are depicted by the lines NF, and the lines of flux due to thedesired signal S are depicted by the lines SF. The potential drop acrosseach of the coils due to the respective fields of flux is depicted bythe plus and minus signs directly below the letters S, L and N which aresituated adjacent each of the coils. The potential drop across the coilsdue to the noise field NF is a follows: There is a potential drop of Nacross the coil 35, +N across the coil 36, -N across the coil 37, and +Nacross the coil 38 which has a net result of zero potential being sensedby the receiver 39 due to the noise field NF. The potential drop acrossthe coils due to the local field LF is as follows: Across the coil 35there is a potential drop of -L across coil 36 +L, across coil 37 +L,and across coil 38 +L which results in a net potential drop of zerobeing sensed by the receiver 39 due to the local field LF. The potentialdrop across the coils due to the desired flux filed SF is as follows:Across the coil 35 there is a potential drop of +8, across the coil 36 apotential drop of +5, across the coil 37 a potential drop of +8, andacross the coil 38 a potential drop of +S which is a resultant potentialdrop of 4S which is sensed by the receiver 39 in response to the desiredflux field SF. The only requirement as far as coil positioning is thatthe coils 35 and 36 be positioned parallel to each other with respect toa plane of reference and that the coils 37 and 38 be positioned parallelto each other with respect to a plane of reference, which may bedifferent than the plane of reference for the coils 35 and 36. If thecoils 35 and 36 are positioned closer to one end of the short circuitmember 34 than the coils 37 and 38 are positioned relative to the otherend of the short circuit member 34, this has no effect on thecancellation of the potential drop since the respective coils cancelonly the potential drop generated by the flux field at their particularend of the short circuit member.

In FIG. 8 there is illustrated how an antenna or receiving coil such asthe coil 41 may be mounted on a rail 42. Such an arrangement may be usedwhen for one reason or another' the coils are not placed upon the shortcircuit member between the rails.

In FIG. 9 there is shown an embodiment in which the antennas orreceiving coils are placed on the conductive rails in a manner asillustrated in FIG. 8. In each rail there are propulsion currents Nflowing in a direction as depicted by the arrows N. Also there arecurrents L flowing in each rail depicted by the arrows L, which aregenerated by the local transmitter. There are also flowing in each railand in the short circuit member 44 the current S generated by thedesired signal which is to be sensed by the receiving coils, and whichis depicted by the lines S in phantom. The fields of flux due to thepropulsion currents or noise currents is depicted by the flux lines NF,the lines of flux due to the local current are depicted by the lines offlux LF, and the fiux field generated by the desired signal S aredepicted by the flux lines SF. Conductive rails 42 and 43 are bondedtogether by the short circuit member 44. The conductive rail 42 hasmounted thereon antennas or receiving coils 45 and 46, and theconductive rail 43 has mounted thereon antennas or receiving coils 47and 48. The potential induced in these coils due to the flux field SF.LF, and NF are depicted by the plus or minus signs under the letter S, Land N, respectively, which are placed adjacent each of the coils. Thepotential drop in each of the coils due to the respective flux fieldswill not be traced. In response to the flux field NF generated by thepropulsion currents N, there is produced across the coil 46 a potentialdrop of N, across the coil 45 a potential drop of +N, across the coil47, a potential drop of N, and across the coil 48 a potential drop of+N, with a resultant potential drop of zero being sensed by a receiver49. In response to the local field LF there is produced across coil 46 apotential drop of -L, across coil 45 a potential drop of +L, across coil47 a potential drop of +L, and across coil 48 a potential drop of L witha resultant potential drop of zero 'being sensed by the receiver 49 inresponse to the local currents L which generated the local field LF. Inresponse to the desired signal S the following potentials are induced inthe coils. Across the coil 46 there is zero potential drop producedsince the current S does not flow through the rail adjacent the coil 46,across the coil 45 there is potential drop of +S, across the coil 47there is a potential drop of +5, and across the coil 48 there is nopotential drop due to the desired signal S since no current from thedesired signal S flows through the rail 43 adjacent the coil 48. Thereceiver 49 therefore senses a potential drop of 28 in response to thedesired signal S. It is readily seen that an arrangement of only twocoils such as the coils 45 and 46 on the rail 42 or alternatively thecoils 47 and 48 on the rail 43 may be used to cancel the potential dropsdue to the local field LF and the noise field NF, since across each railthe field NF and LF produce series opposing relationsbips in the coilsmounted on the respective rails. This could be accomplished byconnecting the line 50 to the terminal of the receiver 49 and removingthe pair of coils on the rail 43. However, in practice an arrangement asillustrated in FIG. 9 is used in conjunction with other apparatus forsensing broken rails along the track.

In summary, a plurality of antenna or receiving coil arrangements,operative with a conductive track system, have been illustrated in whicha first or a desired signal is sensed and at least a second or anundesired signal is not sensed or if sensed is sensed in a seriesopposing relationship in the coils which make up the antennaconfiguration, resulting in substantially eliminating the undesiredsignals.

We claim as our invention:

1. In a signalling system operative with a conductive track, including apair of conductive rails, and a plurality of conductive membersconnected between said rails at predetermined locations, with thesection of track between and including two such conductive membersforming a track circuit signalling block, the combination comprising:

signal transmitting means located adjacent the conductive member formingone end of a given track circuit signalling block for inducing into saidrails a local signal to be sensed in an adjacent track circuitsignalling block;

means for inducing a desired signal into said rails to be sensed in saidgiven track circuit signalling block; and

signal receiving means, including at least first and second signalreceiving antennas being positioned on opposite sides and opposite endsrespectively of said conductive member forming one end of said giventrack circuit signalling block, said first and second signal receivingantennas being aligned substantially parallel to one another withrespect to a reference plane, and being connected to one another inseries such that the signal induced into said first and second signalreceiving antennas by said local signal is in a series opposingrelationship, and the signal induced into said first and second signalreceiving antennas by said desired signal is in a series aidingrelationship.

2. The combination claimed in claim 1, wherein said first and secondsignal receiving antennas comprise first and second coils, respectively,with each coil having first and second terminals, with the secondterminal of the first coil being connected to the first terminal of thesecond coil; and

said signal receiving means further including a signal receiver havingtwo terminals, with one terminal being connected to the first terminalof the first coil, and the remaining terminal being connected to thesecond terminal of the second coil,

3. In a signalling system operative with a conductive track, including apair of conductive rails, and a plurality of conductive membersconnected between said rails at predetermined locations, with thesection of track between and including two such conductive membersforming a track circuit signalling block, the combination comprising:

signal transmitting means located adjacent the conductive member formingone end of a given track circuit signalling block for inducing into saidrails a local signal to be sensed in an adjacent track cir- 8 cuitsignalling block; means for inducing a desired signal from an adjacenttrack circuit signalling block into said rails to be sensed in saidgiven track circuit signalling block;

first, second, third, and fourth coils, the first and second coils beingmounted on opposite sides of one end of said conductive member formingone end of said given track circuit signalling block and being alignedsubstantially parallel with one another with respect to a referenceplane, with said third and fourth coils being mounted on opposite sidesof the other end of said conductive member and being alignedsubstantially parallel to one another with respect to a reference plane,said coils being connected in series such that the signal induced intosaid coils by said local signal is in a series opposing relationship,and the signal induced into said coils by said desired signal is in aseries aiding relationship; and

a signal receiver operative with said first, second,

third, and fourth coils for sensing the signal induced in said coils.

4. In a signalling system operative with a conductive track, including apair of conductive rails, and a plurality of conductive membersconnected between said rails at predetermined locations, with thesection of track between and including two such conductive membersforming a track circuit signalling block, the combination comprising:

signal transmitting means located adjacent the conductive member formingone end of a given track circuit signalling block for inducing into saidrails a local signal to be sensed in an adjacent track circuitsignalling block;

means for inducing a desired signal from an adjacent track circuitsignalling block into said rails to be sensed in said given trackcircuit signalling block; at least first and second coils, the first andsecond coils being mounted on one rail on opposite sides of saidconductive member forming one end of a given track circuit signallingblock and being aligned substantially parallel to one another withrespect to a reference plane, said coils being connected in series suchthat the signal induced into said coils by said local signal is in' aseries opposing relationship, and the signal induced into said coils bysaid desired signal is in a series aiding relationship; and a signalreceiver operative with said at least first and second coils for sensingthe signals induced in said coils.

S. The combination claimed in claim 4 including third and fourth coilsmounted on the other rail on opposite sides of said conductive memberand being aligned substantially parallel to one another with respect toa reference plane, said third and fourth coils being connected in serieswith said first and second coils such taht the signal induced into saidcoils by said local signal is into a series opposing relationship andthe signal induced into said coils by said desired signal is in a seriesaiding relationship.

1. In a signalling system operative with a conductive track, including apair of conductive rails, and a plurality of conductive membersconnected between said rails at predetermined locations, with thesection of track between and including two such conductive membersforming a track circuit signalling block, the combination comprising:signal transmitting means located adjacent the conductive member formingone end of a given track circuit signallinG block for inducing into saidrails a local signal to be sensed in an adjacent track circuitsignalling block; means for inducing a desired signal into said rails tobe sensed in said given track circuit signalling block; and signalreceiving means, including at least first and second signal receivingantennas being positioned on opposite sides and opposite endsrespectively of said conductive member forming one end of said giventrack circuit signalling block, said first and second signal receivingantennas being aligned substantially parallel to one another withrespect to a reference plane, and being connected to one another inseries such that the signal induced into said first and second signalreceiving antennas by said local signal is in a series opposingrelationship, and the signal induced into said first and second signalreceiving antennas by said desired signal is in a series aidingrelationship.
 2. The combination claimed in claim 1, wherein said firstand second signal receiving antennas comprise first and second coils,respectively, with each coil having first and second terminals, with thesecond terminal of the first coil being connected to the first terminalof the second coil; and said signal receiving means further including asignal receiver having two terminals, with one terminal being connectedto the first terminal of the first coil, and the remaining terminalbeing connected to the second terminal of the second coil.
 3. In asignalling system operative with a conductive track, including a pair ofconductive rails, and a plurality of conductive members connectedbetween said rails at predetermined locations, with the section of trackbetween and including two such conductive members forming a trackcircuit signalling block, the combination comprising: signaltransmitting means located adjacent the conductive member forming oneend of a given track circuit signalling block for inducing into saidrails a local signal to be sensed in an adjacent track circuitsignalling block; means for inducing a desired signal from an adjacenttrack circuit signalling block into said rails to be sensed in saidgiven track circuit signalling block; first, second, third, and fourthcoils, the first and second coils being mounted on opposite sides of oneend of said conductive member forming one end of said given trackcircuit signalling block and being aligned substantially parallel withone another with respect to a reference plane, with said third andfourth coils being mounted on opposite sides of the other end of saidconductive member and being aligned substantially parallel to oneanother with respect to a reference plane, said coils being connected inseries such that the signal induced into said coils by said local signalis in a series opposing relationship, and the signal induced into saidcoils by said desired signal is in a series aiding relationship; and asignal receiver operative with said first, second, third, and fourthcoils for sensing the signal induced in said coils.
 4. In a signallingsystem operative with a conductive track, including a pair of conductiverails, and a plurality of conductive members connected between saidrails at predetermined locations, with the section of track between andincluding two such conductive members forming a track circuit signallingblock, the combination comprising: signal transmitting means locatedadjacent the conductive member forming one end of a given track circuitsignalling block for inducing into said rails a local signal to besensed in an adjacent track circuit signalling block; means for inducinga desired signal from an adjacent track circuit signalling block intosaid rails to be sensed in said given track circuit signalling block; atleast first and second coils, the first and second coils being mountedon one rail on opposite sides of said conductive member forming one endof a given track circuit signalling block and being alignedsubstantiaLly parallel to one another with respect to a reference plane,said coils being connected in series such that the signal induced intosaid coils by said local signal is in a series opposing relationship,and the signal induced into said coils by said desired signal is in aseries aiding relationship; and a signal receiver operative with said atleast first and second coils for sensing the signals induced in saidcoils.
 5. The combination claimed in claim 4 including third and fourthcoils mounted on the other rail on opposite sides of said conductivemember and being aligned substantially parallel to one another withrespect to a reference plane, said third and fourth coils beingconnected in series with said first and second coils such taht thesignal induced into said coils by said local signal is into a seriesopposing relationship and the signal induced into said coils by saiddesired signal is in a series aiding relationship.